title: Effect of storage and preservation of milk samples on the response of microbial inhibitor tests.
abstract: The aim of this study was to evaluate the effect of storage time (4 °C) on milk samples and the use of azidiol as preservative on the results of microbial inhibitor tests used to detect antimicrobials in milk. For this purpose, 16 milk bulk samples divided into two aliquots, preservative-free and with azidiol, spiked with 12 concentrations of amoxicillin, ampicillin, penicillin G and oxytetracycline, were used. The milk samples were analysed using the BRT MRL, Delvotest MCS Accelerator and Eclipse 100 at 0, 24, 48 and 72 h stored at 4 °C. The logistic regression model was applied to study the effect of storage time (ST), preservative (P) and their interaction (ST×P). At a concentration equivalent to the Detection Limit (DL), the positive results of microbial inhibitor tests do not remain stable during storage time. These results are more reproducible if samples are stored with a preservative. At Maximum Residue Limits (MRLs) concentration microbial inhibitor tests can detect penicillin for up to 72 h of storage. For oxytetracycline, the BRT MRL and Delvotest MCS tests presents DL exceeding the MRL, therefore they are not sensitivity to this tetracycline (0% positive results). By contrast Eclipse 100, whose DL is lower than the MRL, gave 100% positive results during the 72 h storage period. It can be concluded that it would be convenient to store milk samples with azidiol at 4 °C and to carry out analyses within the first 48 h since milk sampling.
authors.affiliation: Instituto de Ciencia y Tecnología Animal, Universitat Politècnica de València, Camino de Vera, s/n 46022 Valencia, Spain.
authors.forename: Milagro Borràs
authors.initials: MB
authors.lastname: Llopis
authors.forename: Marta Roca
authors.initials: MR
authors.lastname: Marugán
authors.forename: Marta Roca
authors.initials: MR
authors.lastname: Marugón
authors.forename: Rafael Lisandro
authors.initials: RL
authors.lastname: Althaus
authors.forename: Maria Pilar Molina
authors.initials: MP
authors.lastname: Pons
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology; D001978:Bromphenol Blue; D002701:Chloramphenicol; D002951:Citrates; D004350:Drug Residues; D005520:Food Preservatives; D061353:Food Storage / Q000379:methods*; D008892:Milk / Q000737:chemistry* / Q000382:microbiology*; D012034:Refrigeration; D019810:Sodium Azide
chemical_list: D000900:Anti-Bacterial Agents; D002951:Citrates; D005520:Food Preservatives; C000589731:azidiol; D001978:Bromphenol Blue; D002701:Chloramphenicol; D019810:Sodium Azide